A treatment tool for an endoscope, includes a sheath which has a center axis along a longitudinal axis； a pre-curved portion which is disposed at a distal portion of the sheath； a knife wire lumen which has a center axis and is formed along the longitudinal axis； a cutting portion which protrudes from an outer circumference surface positioned at an inward side of the curved shape to outside of the pre-curved portion and extends from a distal end portion toward a proximal end portion of the pre-curved portion； a guide wire accommodation portion which is formed along the longitudinal axis of the sheath； a proximal slit formation portion which is communicated from the guide wire accommodation portion to the outside of the sheath； and a distal slit formation portion which is extended from the proximal end of the pre-curved portion to an intermediate portion of the pre-curved portion.
